1. Field of the Invention
This invention relates to materials and methods for photocatalyzing the oxidation of organic compounds floating on water, such as those typically resulting from an oil spill.
2. Description of Related Art
Oil spills in the world's oceans and seas have a potentially damaging effect on the environment. Oil entering the seas can have a harmful impact not only upon the marine ecosystem, but also upon commercial and recreational resources of coastal areas.
Organic compounds invade the world's waterways from many sources in addition to oil spills. For example, refineries located along rivers often introduce substantial amounts of organic products and waste into the water. Organic compounds from landfills and waste sites can leach down to water tables below the earth's surface. Recreational motorboats often exhaust and leak a certain amount of oil and gasoline into lakes and reservoirs. These are just a few of the sources of organic compounds entering water resources.
The problems associated with petroleum in water may be ameliorated over time through various natural treatment processes. Among these are evaporation, dissolution, dispersion, adsorption onto suspended particulate matter, sinking, and microbial oxidation.
Another naturally occurring process for treating oil films on water is photocatalytic oxidation (alternatively referred to as photoassisted or photochemical oxidation or as photooxidation). Since oil and related organic materials generally have a lower density than water, they tend to float on the surface of water as a film, and are thereby exposed to a significant amount of solar illumination. Natural photocatalytic oxidation of floating oil films has been the subject of several studies, and it is generally known that oxidation of organic compounds in oil can be naturally photocatalyzed and that the oxidation products are generally more water soluble and/or less refractory compounds, such as alcohols, ketones, and carboxylic acids. These photooxidation products may be environmentally less harmful, because after dissolving, they tend to be more readily attacked by microorganisms for eventual complete oxidation to CO.sub.2.
Techniques for cleaning oil slicks have been tried and are discussed in the literature. For example, mechanical clean-up methods, such as the use of booms, skimmers, and absorbents, have been used. However, these are impractical in many situations.
Chemical techniques have also been tried. For example, dispersants and emulsifiers may be used to accelerate natural dispersion of oil. However, these techniques are environmentally damaging in many situations, as they may simply direct the oil and resulting damage away from the water surface to underlying depths.
Another technique which has been suggested is the use of organic photosensitizers to photocatalyze the oxidation of the oil film. A potential problem with this type of technique is that the wavelengths needed to excite the oil-dissolved photosensitizer are often absorbed by other constituents of the oil film. Furthermore, even if the photosensitizer has been excited by a photon, it may be "quenched", i.e. transfer energy to another dissolved compound that is not an adequate photosensitizer. Therefore, this technique has not been widely accepted.
Thus, there is a continuing need for environmentally safe and beneficial methods for treating organic compounds which float on and plague the surface of bodies of water. It is an object of this invention to provide materials and methods for such treatment which overcome or reduce at least some of the disadvantages of the prior art.